Hot fill container

ABSTRACT

A PET hot fill bottle ( 2 ) has a neck ( 3 ) and a body ( 4 ). It is stretched and blown into a cavity ( 14 ), with internal pressure holding the body against the cavity. During a first period, the cavity is heated to 100° to 160° C. for between 3 to 7 seconds to relax stresses in the body. During a second period the cavity is cooled to 60° to 120° C. for 4 to 8 seconds. This solidifies it—without introducing stresses—so that it can be removed from the mould. The resulting bottle is heat stable when filled with water close to its boiling point, namely at 92° C. to 98° C. For the rapid heating and cooling of the mould cavity, it is provided with two series of passages ( 16, 17 ). The former house ohmic heaters ( 18 ); whilst the latter are connected to water and air supply lines ( 19, 20 ).

The present invention relates to a plastics material container which canbe filled with hot liquid.

It is advantageous to be able to fill a container, such as a bottle,with a drink, such as a fruit juice, when hot, because the heat of theliquid both renders it sterile itself and sterilises the bottle.However, there is the disadvantage that the heat may cause the stressheld in the bottle to be relieved, with the result that the bottledistorts. For instance PET (Polyethylene Terephthalate) bottle arenormally temperature stable up to only 60° C.

Techniques for sterilising bottles are as follows:

-   -   Carbonation of the liquid, which is applicable only to soft        drinks and not to non-carbonated beverages,    -   γ radiation, which is expensive;    -   Addition of ozone, which is not possible for drinks including        organic matter;    -   Addition of preservatives, but these tend to be toxic,    -   Hot-fill of glass bottles, typically at between 85°-92° C.

PP (Polypropylene) is heat resistant, but not generally suitable forfoods, due to taste and lack of transparency. PET is a food gradematerial, being approved by the FDA. It has high transparency and nosmell nor taste, but it is not heat reistant at least not inconventional bottle form.

Many attempts have been made to improve the temperature resistance ofPET. Chief amongst these are:

-   -   Addition of PEN (Polyethylene Naphthalate) This polymer is        expensive and difficult to process, with a small processing        window. Further it has a short storage life.    -   Additional processing to relieve the stresses induced in the        polymer by blowing of the bottle. Typically this involves        blowing a bottle which is oversize, applying heat to cause it to        shrink and then blowing it again to the final size. This is        inefficient in requiring the use of TWO moulds and a quantity of        polymer which is adequate for making the oversize bottle.        Further, radiant heat is required in the shrink step.

The object of the present invention is to provide an improved hot-fillbottle and similar containers.

According to a first aspect of the invention there is provided a methodof forming a body of plastics material container consisting in the stepsof.

-   -   blowing a heated, injection moulded preform to finish formed        shape in a mould imparting the finish formed shape to the body        of the container,    -   holding the blown container body in contact with the mould at        elevated temperature for a first period after blowing to allow        internal blowing stresses to relax,    -   reducing the mould temperature and similarly holding the        container body in contact with the mould at lower temperature        for a second period to cool it below its solidification        temperature without internal stressing of the container,    -   removing the container from the mould.

By “solidification temperature” is intended the temperature at or belowwhich the container retains its finish formed shape in ambienttemperature.

Desirably, elevated pressure, conveniently the blowing pressure, ismaintained in the container during the first period.

Preferably, the inside of the container is cooled whilst it is held incontact with the mould during the second period. Conveniently thisinside cooling is by means of cool pressure air circulated within thecontainer body during the second period.

Preferably the container is of PET material.

Preferably the elevated temperature at which the mould—and the containerin contact with the mould—is held is 130° C.±30°. Further, this step ispreferably held for 5±2 second.

Preferably the reduced temperature to which the mould—and the containerin contact with the mould—is cooled is 90° C.±30°. Further, this step ispreferably held for 6±2 second.

Usually, the temperature of the mould will be dropped—from the elevatedtemperature to the reduced temperature—by between 40 & 50 Centigradedegrees.

In the preferred embodiment, the drop in temperature between the twoperiods is achieved by passing water through cooling passages in themould. Thereafter, air is passed through cooling passages in the mouldto maintain the mould temperature for the rest of the cooling period.During the mould cooling period, the interior of the container is cooledby circulation of cool air in the container, although this air is stillmaintained under pressure.

Preferably cooling air is passed through the container during thesecond, cooling period. At the end of the cycle, the mould is reheated,by ohmic heaters, to the elevated temperature.

According to a second aspect of the invention there is provided aplastics material container, the container being substantially free ofinternal, formation stresses whereby it is suitable for hot filling, thecontainer having been formed by the method of the first aspect of theinvention.

According to a third aspect of the invention there is a provided a mouldtool for use in the method of formation and treatment of the body of acontainer of the second aspect of the invention, the mould tool having:

-   -   a blowing cavity;    -   a plurality of cooling passages for water and air circulation;    -   a plurality of heating passages in the mould tool for        circulation of heating fluid and/or for ohmic heaters;    -   a blowing pin arrangeable before the blowing cavity is closed,        in a neck of the container, for its blowing; and    -   a stretch pin extending through the blowing pin for stretching        of the preform.

Preferably, the stretch pin has a plurality of small air circulationapertures for internal cooling of the container.

The cooling water passages are preferably adapted for circulation of airsubsequent to the circulation of water during each moulding cycle.

The heating means may be configured as a plurality of heating passages.

Whilst it is envisaged that the heating passages may be adapted forcirculation of a heating fluid such as oil, in the preferred embodimentthey are adapted to house a plurality of ohmic heaters.

According to a fourth aspect of the invention there is provided a methodof treating the inner neck of a plastics material container, thetreatment consisting in the steps of:

-   -   assembling the neck of a preform of the container to an external        support;    -   applying a heating pin to the inside of the neck for a first        period;    -   applying a cooling pin to the inside of the neck for a second        period;    -   removing the neck preform from the external support.

Normally, the heating and cooling of the inner neck will cause it tobecome heat stable by crystallisation of its inner neck material.

Where the preform is moulded in a production line common with theblowing of the container, the external support may comprise part of amould cavity for the moulding of the neck of the preform. Alternativelythe neck support will be complementarily shaped to the neck for tightsupport thereof. In the preferred embodiment, the support is radiallysplit and itself externally supported by a neck plate.

To help understanding of the invention, a specific embodiment thereofwill now be described by way of example and with reference to theaccompanying drawings, in which:

FIG. 1 is a side view of a hot fill bottle being filled with hot liquid;

FIGS. 2, 3 and 4 are a series of side views of a hot fill bottleaccording to the invention being formed;

FIGS. 5 and 6 are more detailed cross-sectional side and plan viewsshowing temperature control passageways in a mould for shaping thebottle.

FIGS. 7 and 8 are cross-sectional side views of a heat treatment jig ofthe inside of a preform neck; and

FIG. 9 is a view similar to FIG. 4 on a larger scale.

Referring first to FIG. 1, there is shown a hot fill container 1 in theshape of a bottle 2 having a neck 3 and a body 4. FIG. 1 shows thebottle being filled with a hot water based liquid 5, close to boilingpoint. The liquid is sufficiently hot, typically 95° C. to substantiallysterilise the inside of the bottle. If the bottle had beenconventionally formed of PET material, at this temperature, anysubstantial stresses remaining in the bottle as a result of itsstretching and blowing would be liable to cause it to contract to asmaller size. The extent and locality of the contraction isunpredictable. The invention is concerned with eliminating thesestresses.

FIG. 2 shows a preform 11 in a neck support 12 assembled to the mouth 13of a blow mould cavity 14 for providing a bottle of the invention withits finish formed shape. The preform is hot, typically around 160°C.—either having been injection moulded immediately prior to assembly tothe blow mould cavity or having been reheated, see below—and the blowmould cavity is at approximately 130° C. ±30. By means of a stretch pin15 provided with a series of small apertures and application of internalgas pressure, the preform is stretched and blown to its finish formedshape, see FIG. 3. Maintaining the pressure of the gas G in the bottleafter blowing holds its body 5 in contact with the blow mould cavity andraises its temperature to that of the cavity. To speed the heating, thegas atmosphere 6 within the bottle can be circulated with hot air passedinto the container around the stretch pin and out through it, thestretch pin being provided with a series of small apertures 15A. Thebody of the bottle is maintained at the elevated temperature forsufficient time to relax any stresses resulting from the stretching. Atemperature range of between 100° C. and 160° C. and holding the body atthis temperature for between 3 to 7 seconds is expected to be effectivein stress relaxation.

Opening of the mould to release the bottle at this temperature wouldresult in it being too hot to maintain its finish formed shape.Accordingly, the mould is cooled to between 60° C. and 120° C. for 4 to8 seconds, see FIG. 4. During this period cool air is circulated intothe container and out through the small apertures in stretch pin, withpressure being maintained in the container. This solidifies it withoutintroducing stresses—so that it can be removed from the mould. Theresulting bottle is heat stable when filled with water close to itsboiling point, namely at 92 to 98° C.

For the rapid heating and cooling of the mould, it is provided with twoseries of passages 16, 17. The former house ohmic heaters 18, whilst thelatter are connected to water and air supply lines 19, 20.

After opening of the mould, the heaters 18 are switched on to rapidlyheat it to the elevated temperature. A preform is assembled at its neckin the mouth of the mould, with the support 12 abutting a seat 21 in there-closed mould. The preform is stretched and blown. The mould isthermostatically controlled to the elevated temperature, with theheaters being switched off at the end of the first period. By operationof ganged valves 22, cooling water is immediately passed through thecooling passages 17 to drop the temperature to its reduced level, tosolidify fully the body of the container. In order to avoid dropping thetemperature too much, in view of the need to reheat it again for thenext cycle, the valves are operated during the cooling period to replacethe water circulation by air circulation in the passages 17. At the sametime, the cool air is circulated under pressure inside the bottle tocool the inside of the body.

Turning now to FIGS. 7 & 8, the jig thereshown accommodates a preform 11in a block 51 with heaters 52 for preheating the preform prior to itsstretching and blowing. The neck of the preform is held in a radiallyparting support 53 located in an outer holding ring 54. For heattreatment of the inner neck in like manner to that of the body of thebottle, firstly a heating pin 55 is inserted into the neck to raise itstemperature to the region of 120° to 160° C.—as shown in FIG. 7—to relaxthe internal stresses. After a first period, the heating pin is removedand replaced by a cooling pin 56 to cool the neck to the region of 60°to 100° C. as shown in FIG. 8.

Once the cooling pin has been withdrawn, the new preheated preform ismoved with the support 53 to the mould 14 for stretch-blowing and heattreatment. Once the support 53 is positioned at the mouth of the blowmould, a blowing pin 65 is advanced into the neck of bottle. The stretchpin 15 is then advanced through the blowing pin, as shown in FIG. 9,which shows essentially the same as FIG. 4 but in greater detail. Thebottle is then formed as described above.

1. A method of forming a plastics material container comprising thesteps of: blowing a heated, injection moulded preform to finish formedshape in a mould imparting the finish formed shape to the body of thecontainer, holding the blown container in contact with the mould atelevated temperature for a first period after blowing to allow internalblowing stresses to relax, passing water through the mould so as toreduce the mould temperature to a lower temperature, after passing thewater through the mould, passing air through the mould so as to hold themould at the lower temperature for a second period, holding thecontainer in contact with the mould during said second period to coolthe container below its solidification temperature without internalstressing of the container, and removing the container from the mould.2. A method as claimed in claim 1, wherein elevated pressure ismaintained in the container during the first period.
 3. A method asclaimed in claim 1, wherein elevated pressure is maintained in thecontainer during the second period.
 4. A method as claimed in claim 1,wherein the inside of the container is cooled while it is held incontact with the mould during the second period.
 5. A method as claimedin claim 2, wherein the elevated pressure is the pressure at which thepreform is blown.
 6. A method as claimed in claim 1, wherein thematerial of the container is PET material and the elevated temperatureat which the mould is held is 130° C.±30° C.
 7. A method as claimed inclaim 6, wherein the elevated temperature is held for a first period of5±2 seconds.
 8. A method as claimed in claim 1, wherein the material ofthe container is PET material and the reduced temperature to which themould is cooled is 90° C.±30° C.
 9. A method as claimed in claim 8,wherein the reduced temperature is held for a second period of 6±2seconds.
 10. A method as claimed in claim 1, wherein the temperature ofthe mould is dropped—from the elevated temperature to the reducedtemperature—by between 40 & 50 Celsius degrees.
 11. A method as claimedin claim 1, wherein the mould is reheated, by ohmic heaters, to theelevated temperature after the second, cooling period.